BOSTON The painstaking work to identify a bombing suspect from reams of Boston Marathon footage yielded a possible breakthrough as investigators focused on a man seen dropping off a bag, and then walking away from the site of the second of two deadly explosions.

CBS News correspondent Bob Orr reports investigators are hoping cell phone records may produce an identification of the mystery man in the surveillance pictures. Investigators are scouring cell phone logs to find out who made calls from the site of the second explosion around the time the bombs went off.

The discovery of the image — found on surveillance footage from a department store near the finish line — was detailed by a city politician two days after the attack that left three people dead, wounded more than 170, and cast a dark shadow over one of this city's most joyous traditions.

Meanwhile, Homeland Security Secretary Janet Napolitano said Thursday the FBI wants to speak with individuals seen in at least one video from marathon, but she says she isn't calling them suspects. Without providing details of the men's appearance or what the video shows, Napolitano told the House Homeland Security Committee on Thursday that "there is some video that raised the question" of individuals the FBI would like to interview. She said the investigation is continuing "apace."

Investigators are focusing on the man spotted near the scene of the second explosion, Orr reports. Sources say a nearby surveillance camera captured images of the man carrying a backpack and talking on a cell phone. While the FBI has not identified him, he's described as a young white man as tall as 6 foot 2.

Sources who have seen the tape say he appeared to be alone and was wearing a black jacket, gray hoodie and white baseball cap backwards on his head, Orr reports. Sources told Orr the man appeared to place his backpack on the ground, then after the first explosion, he fled. Moments later the second blast occurred near the spot where he had been standing.

The footage hasn't been made public but former FBI assistant director John Miller said on "CBS This Morning" that the public can expect to see more photos to be released of the possible suspect seen with a backpack.

CBS Web Copy

Updated at 2:45 p.m. ET

Authorities investigating the deadly bombings at the Boston Marathon have zeroed in on a man seen on surveillance video near the site of the attack.

CBS News correspondent Bob Orr reports that authorities have spotted at least one person they want to speak with, either as a witness or as a possible suspect. At this point, federal officials say, no arrests have been made.

At the site of what became the second explosion on Monday, surveillance video captured a white man placing a backpack on the ground while talking on a cell phone, sources told Orr. The man was wearing a black jacket, a grey hooded sweatshirt and a white or offwhite baseball cap on backwards. He is 6 feet tall or 6-foot-2 with a medium build.

While the man was on the phone, the first explosion went off.

Investigators focused on the timeframe of that call and retrieved cell-phone information from that period to identify potential call users. Authorities then matched up the users' identities with pictures and video footage to zero in on a suspect.

CBS News senior correspondent John Miller reports that authorities settled on one individual late Tuesday and are having discussions over whether to go public with identifying the person.

Meanwhile, investigators have found the lid of a pressure cooker that apparently was catapulted onto the roof of a nearby building, a law enforcement source said Wednesday.

The law enforcement source confirmed to CBS News senior investigative producer Pat Milton Wednesday that the lid was found on the top of a building near the attack site.

Associated Press Release By DENISE LAVOIEAP Legal Affairs Writer

BOSTON (AP) -- Federal officials are denying that a suspect is in custody in the Boston Marathon bombings.

A law enforcement official briefed on the investigation told The Associated Press on Wednesday a suspect was in custody.

But the FBI and the U.S. attorney's office in Boston dispute that.

The official who spoke to The Associated Press did so on condition of anonymity and stood by the information even after it was disputed.

The official was not authorized to divulge details of the investigation. The official had said the suspect was expected in federal court in Boston.

By DENISE LAVOIEAP Legal Affairs Writer BOSTON (AP) -- A law enforcement official briefed on the investigation says a suspect in the Boston Marathon bombings is about to be arrested.

The official spoke to The Associated Press on condition of anonymity Wednesday. The official was not authorized to divulge details of the investigation.

The official says the suspect is to be taken into custody by federal marshals and taken to a Boston courthouse.

Law enforcement agencies had earlier pleaded for the public to come forward with photos, videos or any information that might help them solve the twin bombings that killed three people and wounded more than 170 on Monday.

Investigators circulated information about the bombs, which involved kitchen pressure cookers packed with explosives, nails and other lethal shrapnel. But the FBI said nobody had claimed responsibility.

CNN is reporting that an arrest has been made in the Boston Marathon bombings.

(CNN) -- Investigators believe they have identified a suspect in the Boston Marathon bombings, a source who has been briefed on the investigation told CNN's John King exclusively.

The breakthrough came from analysis of video from a department store near the site of the second explosion. Video from a Boston television station also contributed to the progress, said the source, who declined to be more specific but called it a significant development.

Earlier, a federal law enforcement source with firsthand knowledge of the investigation told CNN that a lid to a pressure cooker thought to have been used in the bombings had been found on a roof of a building near the scene.

While such clues may move the investigation forward, they did not reveal whether the attack was an act of domestic or foreign terrorism.Tracking suspects in the Boston bombingsNew clues in Boston Marathon attackPhotos: Deadly attack at Boston Marathon Photos: Deadly attack at Boston Marathon

"If your experience and your expertise is Middle East terrorism, it has the hallmarks of al Qaeda or a Middle East group," former FBI Assistant Director Tom Fuentes said. "If your experience is domestic groups and bombings that have occurred here, it has the hallmarks of a domestic terrorist like Eric Rudolph in the 1996 Atlanta Summer Olympics bombings."

Associated Press ReleaseBy EILEEN SULLIVAN

WASHINGTON (AP) -- Authorities investigating the deadly bombings at the Boston Marathon have recovered a piece of circuit board that they believe was part of one of the explosive devices, and also found the lid of a pressure cooker that apparently was catapulted onto the roof of a nearby building.

A law enforcement official briefed on the investigation confirmed to The Associated Press on Wednesday that authorities have recovered what they believe are some of the pieces of the explosive devices. The official spoke on condition of anonymity because this person was not authorized to publicly discuss evidence in the ongoing investigation.

A person close to the investigation previously told AP the bombs consisted of explosives put in 1.6-gallon pressure cookers, one with shards of metal and ball bearings, the other with nails.

Associated Press Release

BOSTON (AP) -- Federal agents are zeroing in on how the Boston Marathon bombing was carried out, but there's still no word on who did it and why.

An intelligence bulletin issued to law enforcement and released late Tuesday includes a picture of a mangled pressure cooker and a torn black bag. The FBI says evidence indicates the bomber packed a pressure cooker with explosives, nails and ball bearings and hid it in a back pack. The agency says the second bomb was in a metal container, but there isn't enough evidence to indicate that it was a pressure cooker.

The FBI and other law enforcement agencies continue to ask members of the public to come forward with photos, videos or anything suspicious they might have seen or heard.

Many of the more than 170 wounded remain in hospitals, many with serious injuries. A 9-year-old girl and 10-year-old boy are among 17 victims listed in critical condition.

The three people killed include an 8-year-old boy, a 29-year-old woman and a graduate student from China.

The FBI agent in charge says "the range of suspects and motives remains wide open."

Associated Press Release

WASHINGTON (AP) -- An intelligence bulletin issued to law enforcement includes a picture of a mangled pressure cooker and a torn black bag that the FBI says were part of a bomb that exploded during the Boston Marathon.

The bulletin was obtained by The Associated Press.

The FBI says it has evidence that indicates one of the bombs that exploded in the Boston Marathon was contained in a pressure cooker with nails and ball bearings, and it was hidden in a backpack.

The FBI says the other explosive was in a metal container, but there wasn't enough evidence to indicate that it was a pressure cooker.

It was not known what was used to set off the two explosives that killed three people Monday and injured more than 170 others.

Online Public Information File

Viewers with disabilities can get assistance accessing this station's FCC Public Inspection File by contacting the station with the information listed below. Questions or concerns relating to the accessibility of the FCC's online public file system should be directed to the FCC at 888-225-5322, 888-835-5322 (TTY), or fccinfo@fcc.gov.